This invention relates generally to an electron gun and more particularly to an electron gun for projecting a laminar flow rectangular beam in the form of a sheet of electrons.
Rectangular or sheet beam electron guns of the prior art have utilized a cathode forming a circular electron beam which is then shaped by using intercepting apertures and/or two-dimensional electrostatic or magnetic lenses to form the sheet beam. This technique can be used only with relatively low current density beams and has a relatively low efficiency for beam transmission in view of the interception of the beam by the apertures. Another type of sheet beam gun of the prior art has utilized rectangular electrode structure which forms a beam which is magnetically or electrostatically focused during or after the beam leaves the accelerating portion of the gun. Neither of the techniques described above provides a high efficiency laminar flow sheet beam which is sharply focused on a distant target where no focusing or confining electrostatic or magnetic field is required after the beam leaves the gun.